1. Field of the Invention
The present invention relates to an image pickup apparatus which can wireless-communicate with another apparatus.
2. Description of the Related Art
In recent years, a wireless communicating apparatus is installed into a digital still camera (hereinbelow, referred to as a camera), so that the camera and a camera accessory wireless-communicate with each other, thereby enabling them to mutually control. At the time of the wireless communication, a communication module of the camera or camera accessory which is driven is made to periodically transit to a sleep state, thereby suppressing stand-by electricity consumption to a value smaller than that in a communication always-active state.
However, by using the sleep state, timing when the camera and the camera accessory can communicate is limited. Therefore, if a transmission side transmitted a command to a reception side in the sleep state, the reception side cannot receive the command until it is returned back to the communication active state from the sleep state. There is, consequently, a case where timing at which the reception side executes the command from the transmission side is delayed.
For example, when a light emitting command is transmitted from the camera to a flash device serving as a camera accessory, even if the light emitting command was transmitted from the camera for a period of time during which the flash device is in the sleep state, the flash device cannot receive the light emitting command until the flash device is returned back to the communication active state from the sleep state. Therefore, there is a case where timing at which the flash device emits light is delayed, so that there may be a possibility that a synchronization between the camera and the flash device becomes impossible. The “synchronization” is used here to denote a state where the light of a necessary amount can be exposed to an image pickup element of the camera for a period of time during which a shutter of the camera has fully been released. However, if the flash device is set into the communication always-active state in order to perform the synchronization, the stand-by electricity consumption becomes larger than that in the case of using the sleep state.
Therefore, it is necessary to consider a wireless communication system in which while suppressing the stand-by electricity consumption as much as possible, a delay of an execution timing of a predetermined processing is not caused between the camera and the camera accessory.
In the Official Gazette of Japanese Patent Application Laid-Open No. 2006-314093, there has been proposed a control method whereby, in an information processing apparatus, a period of a sleep state is controlled according to permission/inhibition of reception of data of the reception side or an electric power supply amount of a power source unit, thereby minimizing electricity consumption. In the Official Gazette of Japanese Patent Application Laid-Open No. 2006-148471, there has been proposed a control method whereby in order to shorten, as much as possible, a time required for information processing apparatuses to perform a pairing, a period of a sleep state is shortened when a mode is switched to a pairing mode.
However, the method proposed in the Official Gazette of Japanese Patent Application Laid-Open No. 2006-314093 is the control method for minimizing the electricity consumption of the information processing apparatus and does not eliminate a delay of timing at which a predetermined processing is executed between the information processing apparatuses.
According to the method proposed in the Official Gazette of Japanese Patent Application Laid-Open No. 2006-148471, in order to allow the information processing apparatus to find, as fast as possible, the partner to which the pairing is performed, the period of the sleep state is shortened in the pairing mode. In other words, the content disclosed in this patent document is that when the mode is switched to the pairing mode, the period of the sleep state is shortened momentarily, and it does not intend to eliminate a delay of timing at which a predetermined processing is executed between the information processing apparatuses after that.